(1) Field of the Invention
The present invention relates generally to rebonded foam materials and, more particularly, to a process and composition for producing a rebonded foam product having improved flame retardancy properties.
(2) Description of the Prior Art
Polyurethane foam is widely used as cushioning or padding materials. However, because of its cost, there is a significant market for rebonded waste foam chips. Because of the eclectic appearance of rebonded foam, it is usually used where it is not readily seen, for example, as carpet pads and upholstery. Conventionally, rebonded foam is made by shredding and grinding waste polyurethane foam to form polyurethane foam particles, mixing the polyurethane foam particles with a binder, and then curing the binder by one of a number of means, including steam. Accordingly, rebonded foam generally has a relatively high and non-uniform density. Over the years there have been various modifications of the rebonding foam process. Examples of such improvements are described in U.S. Pat. Nos. 3,790,422, 3,894,973, and 4,014,826.
Because of the danger of fire, foam products are often treated with a flame retardant. However, when fabricating rebonded foam, it has generally been possible to incorporate only relatively low amounts of flame retardant materials into the foam to render the resultant foam flame retardant. When large amounts are flame retardant materials are added, the resulting foam generally has poor physical characteristics.
Various means have been tried to improve the flame retardancy of foam and rebonded foam products. For example, U.S. Pat. No. 4,385,131 is directed to the inhibition of smoldering. The resistance to smoldering is achieved by mixing a smoldering agent, e.g., urea, melamine, or a combination thereof, in quantities of at least 40 parts by weight of the smoldering agent to 100 parts of foam chips. A binder is then added to hold the chips and agent together. The mixture is then compressed and cured.
In addition, U.S. Pat. No. 4,438,220 is directed to use of large amounts of solid flame retardant to prevent combustion. This patent is sometimes referred as the "foam-in-foam" patent or the "foam filled foam" patent. Under this approach, the rebonded foam is made by shredding or grinding foam, mixing a solid flame retardant material, and incorporating the mixture of shredded foam and flame retardant material to a new foam formed by polyol and polyisocyanate with enough added water to cause foaming.
In addition to the above patents, various systems have developed for imparting fire retardancy to other polymeric materials. For example, U.S. Pat. No. 4,764,539, issued to Ledane, discloses a combination of materials which imparts superior fire retardant properties to organic polymers. The composition is made up of an organophosphate plasticizer, aluminum hydroxide or aluminum hydrate, amino trioxide, a borate, a bromated hydrocarbon, and a chlorinated paraffin.
U.S. Pat. No. 4,182,799, issued to Rodish, discloses a flame retarding additive for foam polystyrene which is composed of 40-50 weight percent halogenated hydrocarbon, 9-15 weight percent of antimony oxide, 14-22 weight percent of zinc borate, and 16-28 weight percent hydrated alumina.
Finally, U.S. Pat. No. 4,089,912, issued to Levea, discloses a polymer system which incorporates a flame retarding system made up of antimony trioxide and a bromine containing organic compound. Levea also teaches a flame retardant such as zinc borate or the like to be used in place of antimony trioxide either in whole or in part.
Thus, attempts to impart flame retardancy to polymeric materials such as rebonded polyurethane foam have generally been limited to incorporating various percentages of brominated phosphorous combinations in liquid form and by introducing solid compounds such as melamine, antimony oxide, hydrated alumina and others.
Furthermore, with the advent of more stringent fire retardancy requirements, such as the ASTM-E-162 Radiant Panel Test, achievement of low Flame Spread Index (I.sub.s) values requires the inclusion of a high percentage of solids to the foam mass. However, it has been generally necessary to use an organic vehicle such as methylene chloride to impregnate the foam chips with the flame retardant agents. However, methylene chloride requires special handling both to prevent contact with skin and to provide adequate ventilation. In instances where water has been used as a vehicle for impregnating the foam chips with flame retardant agents, it has been limited to water soluble fire retardants such as urea.
These systems have significant drawbacks As discussed above, the use of chlorinated solvents in industrial processes is being severely limited due to potential safety and environmental hazards. In addition, rebonded foam composites made with water soluble agents are not commercially acceptable due to the field migration of the agents, loss of the flame retardancy properties, and contamination of the surfaces on which the foam comes in direct contact due to dusting. Further, rebonded foam composites manufactured with a sufficiently high loading of solid fire retardant agents generally do not produce acceptable physical properties due to particle interference with the adhesive used to rebond the foam chips. In addition, the solid flame retardant agents generally fail to penetrate the cell structure of the foam chip, thereby causing the foam mass to often exhibit a flash phenomena which when exposed to a heat source for an extended period of time.
Thus, it has become desirable to develop a flame retardant system for rebonded foam which eliminates the need for dangerous chlorinated solvents and undesirable hydrated alumina while, at the same time, producing a rebonded foam material of commercially acceptable physical properties and low Flame Spread Index values.